Stormy weather was unleashed in Tesla longsville today when the company’s veteran director of battery technology, Kurt Kelty, unexpectedly resigned to “explore new opportunities”, abruptly ending a tenure with the company that stretched for more than a decade, and comes at a critical time for Elon Musk: just as Tesla enters “production hell” after it delivered its first Model 3 electric car to the general public with a dramatic production ramp up expected in the coming weeks. Kelty joined Tesla in 2006 and was one of the longest-serving executives at Tesla after Elon Musk.

Kurt Kelty is seen at the company’s new sales outlet in Osaka, Japan’s in August 2015

“We can confirm that Kurt Kelty has left the company to explore new opportunities and we want to thank him for everything he’s done for Tesla,” the company told Bloomberg in an emailed statement, adding that his responsibilities will be “distributed among Tesla’s existing teams.”

Ominously, Kelty previously worked for 14 years at Panasonic, Tesla’s critical partner on the battery-producing gigafactory in Reno, Nevada. Kelty was the Tesla point man in negotiations with Panasonic on the plant, according to his LinkedIn profile.

Tesla remains so reliant on its battery technology, or lack thereof, that last month when Tesla failed to meet expected Q2 deliveries of its Model S and Model X cars, it blamed a “temporary shortage of 100 kWh battery packs.”

Tesla and Kelty’s previous employer Panasonic have had a close partnership, with the two in a supply agreement for 1.8 billion battery cells through 2017 for the Model S and Model X. For the Model 3, the companies jointly developed new, slightly larger cylindrical battery cells than those used in Tesla’s existing models.

Adding to Tesla’s headache, Tesla hopes to make 20,000 Model 3 cars per month by December, a ramp-up phase that Musk described to employees as “production hell.”

Kelty is the latest in a long-list of Tesla executives to have departed the company, with at least 20 names counted in just the past 12 months in the following list of TSLA executive departures compiled by @WallStCynic. While the real reason for Kelty’s departure remains unknown, judging by the list below, shortsville may just end up having the final laugh.

Tesla reports Q2 earnings tomorrow after the bell: the circumstances around Kelty’s departure will be one of the key questions asked.